1. Field of the Invention
The present invention relates to an improved apparatus for determining the charge of aqueous suspensions of finely divided, solid, charged particles which determination can be utilized in the continuous regulation of the flocculation of the finely divided charged particles.
2. General Background
It is conventional practive in clarifying aqueous systems containing suspended particles to employ a flocculation operation. Once flocculated, the suspended particles can be separated from their fluid medium by sedimentation, filtration, floatation, centrifugation or one or more of the foregoing physical separatory processes in combination. Conventionally, the flocculation operation is promoted by the use of flocculating chemicals such as alum, ferric chloride or various polymeric materials such as water-soluble cationic and anionic organic polyelectrolytes. Aqueous suspensions of finely divided polymeric particles are encountered in a paper machine headbox within a paper manufacturing process operation and in many other contexts. In a typical flocculation process for flocculating aqueous suspensions of finely divided particles, a water-soluble cationic flocculating chemical is added to the solution. The finely divided particles suspended in the solution are normally negatively charged and thus, the addition of the cationic agent results in charge neutralization on the suspended particles. When the average charge is zero, or some other predetermined value, the dispersed organic and/or inorganic particles undergo flocculation, i.e. aggregation at an optimum rate. Too much cationic agent, however, creates positively charged particles which can be as difficult to flocculate as are the originally negatively charged particles.
To date, however, determining how much chemical to add to the stream to be treated has been difficult, especially since the composition of such stream often varies over fairly wide ranges and time intervals of a few minutes to a few hours.
Various empirical approaches to "finding" the correct dosage of flocculant to be added to a stream have been used. For example, increasing amounts of flocculant may be added to samples from the stream and the amount of decrease in turbidity of the stream noted, the correct dosage being determined as the one which causes the greatest decrease in turbidity with the least addition of flocculant. Such a procedure is time consuming and therefore not really suitable where the composition of the treated solution varies, since the information resulting from this procedure is no longer valid or applicable to the treated solution since the composition of the treated solution will have varied by the time the data has been corrected. The present invention has a built-in early warning system which alleviates this problem.
Another approach is to use a so-called Zeta meter to determine the charge condition existing in the stream. The Zeta meter is used to observe the time required for a charged particle from the stream to pass a predetermined distance along a liquid path while under the influence of an electric field. This method is time consuming and requires a technician to perform the test and to interpret test results before the stream is treated with a greater, lesser, or the same amount of flocculant as had been used since the last previous Zeta meter test was made.
The usual methods of determining the dosage of flocculant to be added to a stream having suspended charge particles are discontinuous and require a substantial amount of individual labor is making the test. The use of such tests in controlling flocculation of such streams is costly both from the standpoint of the labor involved and from the fact that the amount of flocculant actually required by the stream may vary from that indicated by the test.
Accordingly, a principal object of the present invention is to provide an improved instrument which is useful controlling the dosage of chemicals to be added to a controllable stream having a charged condition existing therein.
A further object of the present invention is to provide an improved instrument which is capable of developing, on a continuous basis, an electrical signal which is a function of the charge condition existing in a stream containing charged particles therein.
In accordance with the present invention there is provided a cross-shaped member with a cross-member element and a longitudinal element. Said longitudinal element is provided on its lower end with ingress means for allowing the intake of a sample stream of fluid containing charge-influencing species. The cross-member element is provided with egress means on one end thereof for allowing the outflow of the sample stream. The cross-shaped member is bored through its cross-member and longitudinal elements. A metal tube is disposed in the bore of the longitudinal element of said cross-shaped member, forming a chamber between the outer surface of the metal tube and the inner surface of the longitudinal element. The metal tube extends through the top end of the longitudinal element for mating with a meter/recorder box. A cylindrical, dielectric sleeve is disposed in the bottom of the bore of the metal tube and in fluidly sealing engagement thereto. The dielectric sleeve is adapted for receiving a piston which is connected by a shaft to the inside of the meter/recorder box, the shaft being connected to a rotatable cam driven by an electric motor enclosed by said meter/recorder box. The dielectric sleeve comprises a first ring electrode element in its upper end and a second ring electrode element in its lower end. When turned on, the electric motor inside of the meter/recorder box imparts a torque to said rotatable cam thereby causing said piston to reciprocate within said dielectric sleeve, the stroke of said piston generating a reciprocating shear force against, and thereby generating an electron flow within, a streamed flow of the sample stream which is being pumped or force-fed through said ingress means into the bore of said longitudinal element, through said chamber, and through apertures provided in said metal tube above said dielectric sleeve, and thus, into the bore of said dielectric sleeve. An insulated electrical wire, or first lead wire leads from said first electrode, and a braided shield wire, or second lead wire leads from said second electrode, through a channel provided in said dielectric sleeve and up along the inner surface of said metal tube and through an aperture provided at some arbitrary point near the top of said metal tube, ultimately connecting to circuitry provided in the meter/recorder box. The electron flow generated within the sample stream by the reciprocating shear force of the piston moving up and down within said dielectric sleeve is measured by means of the electrical signal thereby generated across said electrodes travelling through said lead wires, and through the circuitry provided inside of the meter/recorder box. Said circuitry converts said electrical signal into a readable form which is representative of the average electrical charge of the suspended particles in said sample stream.
The present state of the art has advanced to a point similar to the above described apparatus. However, nothing in the prior art has been practically operable due to accumulated particle buildup from the sample stream on the walls of the receiving tube. It is a major objective of the present invention to eliminate this problem which makes these devices impractical to use. The present invention employs an ultrasonic cleaning device which, in accordance with the present invention, is mounted onto the cross-member element of said cross-shaped member on the opposite end thereof from the egress means for said sample stream. Said ultrasonic cleaner which is commercially available, generates mechanical vibrations or shock waves through and around the receiving tube, or dielectric sleeve, thereby preventing particle buildup on the walls thereof. As a result, an accurate determination and reading of the electric potential or charge of the sample stream is facilitated. Further, the present invention employs an optical isolator device inside of the meter/recorder device to facilitate synchronous rectification of the alternating current signal developed across said electrodes. This optical isolator device replaces the magnetically actuated switches employed in the prior art which wear out easier and do not function as well as the optical isolator device of the present invention.
Any additional objects and advantages of the present invention as above briefly described will be best understood when the following detailed description is read in connection with the accompanying drawings, in which: